What happens if the lights go out for days? Britain's 'Black Sky' plan

Imagine your phone has no signal, your taps run dry and the streetlights are off. That is the nightmare behind a "Black Sky" event: a long, widespread loss of power, water and communications. The UK government wants the country to be able to cope for at least 72 hours.

What happened in Lancaster?

It is not just theory. On 5 December 2015, the River Lune flooded and the power went out for about 61,500 people in Lancaster. Engineering professor Roger Kemp was halfway through a Scandi crime drama when it all went dark. He compared the scene to "a zombie movie".

Households lost light and heat. Some water supplies failed because they relied on electric pumps. The railway station, petrol stations and shops closed, most cash machines stopped working and traffic lights failed.

Only two communication systems survived: copper-wire landlines and FM radio. A local station with a generator became the most reliable source of news.

What is the plan now?

The government's "Be Prepared" campaign urges people to stock up, and in a major emergency you would be told to turn on an FM radio. It says there is no specific threat to the grid.

The BBC has its own Black Sky plan. About 100 staff would run an emergency radio studio with secure lines that do not depend on the internet. It would have fuel, water and food for at least three days.

It would broadcast pre-arranged government messages, already published online. They cover how much to drink each day and how to dispose of toilet waste without flushing. Transmitter towers would run on diesel generators for around three days.

The latest advice from Neso (the National Energy System Operator) is that power could probably be back in two to three days.

Why are people worried?

The mass blackout across Spain, Portugal and south-western France in April 2025 pushed the issue up the agenda. Lord Harris, chair of the National Preparedness Commission, warns that power cuts also stop water supplies, and that sewage can back up without moving water.

He also says efficiency drives have stripped out backup systems. He points to emergency services moving from radio to mobile network technology. The government insists 4G and 5G are resilient and reliable.

There is also a £70m project to build planes, known as HAPS, that could circle over the UK and provide at least a week of emergency mobile and internet coverage.